1. Field of the Invention
The present invention is related to an optical transceiver which carries out bi-directional communication simultaneously with the same or different wavelengths using one optical fiber for transmission and reception, or an optical transceiver which carries out reading and writing operations on an optical disc.
2. Description of the Prior Art
The prior art will be described with reference to FIG. 1a and FIG. 1b. FIG. 1a is a rough explanatory drawing of an example prior art optical transceiver, and FIG. 1b is a rough explanatory drawing of a main portion thereof. This prior art example is an optical transceiver which is used in a same wavelength, time division multiplexing, single-fiber bi-directional transmission system.
Namely, the same wavelength, time division multiplexing, single-fiber, bi-directional transmission system is a system which uses the same wavelength for the upstream signals and the downstream signals, and refers to a system in which the transmission and reception times of the upstream signals and the downstream signals are divided periodically, with the upstream signals being transmitted during a certain time period, and the downstream signals being transmitted during another time period, whereby a bi-directional transmission of upstream signals and downstream signals is achieved by a single fiber.
In FIG. 1a, roughly half of the reception signal light from an optical transmission path 10 condensed by a coupling lens 61 passes through a half mirror 62 and is received by a light receiving element 63. Further, roughly half of the transmission signal light from a light emitting element 64 is reflected by the half mirror 62 and condensed in the optical transmission path 10 by the coupling lens 61.
In FIG. 1b, when the transmission signal light beam from the light emitting element 64 expands, a portion of the transmission signal light from the emission port of the light emitting element 64 passes through the half mirror 62 and is incident on the light receiving element 63. In the same wavelength, time division multiplexing, single-fiber, bi-directional transmission system, because the time period for transmitting and receiving the upstream signals and the time period for transmitting and receiving the downstream signals are separated, in principle, even when a portion of the transmission signal light from the light emitting element 64 reaches the light receiving element 63, there will be no interfere with reception. However, when high-level reception signal light is incident on the light receiving element during the transmission state, the reception circuit is temporarily blinded, and there is the risk that reception can not be carried out normally at the time when operations switch from the transmission state to the reception state.
Further, in a same wavelength, direction division multiplexing, single-fiber, bi-directional transmission system, or in a wavelength division multiplexing, single-fiber, bi-directional transmission system, because the upstream signals and the downstream signals are simultaneously transmitted and received, in the structure shown in FIG. 1a and FIG. 1b, a portion of the transmission signal light from the light emitting element 64 reaches the light receiving element 63, and this forms near-end crosstalk. For this reason, it is not possible to apply the optical transceiver having the prior art structure shown in FIG. 1a and FIG. 1b. 
Furthermore, the same wavelength, direction division multiplexing, single-fiber, bi-directional transmission system uses the same wavelength for the transmission and reception of the upstream signals and the transmission and reception of the downstream signals, and refers to a system in which an optical coupler such as a half mirror or the like is used to transmit and receive the upstream signals and the downstream signals simultaneously in order to achieve a bi-directional transmission by a single fiber. Further, the wavelength division multiplexing, single-fiber, bi-directional transmission system uses different wavelengths for the transmission and reception of the upstream signals and the transmission and reception of the downstream signals, and refers to a system in which a wavelength filter is used to transmit and receive the upstream signals and the downstream signals simultaneously in order to achieve a bi-directional transmission by a single fiber.